1. Technical Field of the Invention
The present invention relates generally to a common rail fuel injection system designed to ensure the stability of operation of an engine in the event of an operating problem.
2. Background Art
There are known accumulator fuel injection systems designed to inject fuel into an internal combustion engine at high pressure through a common rail. Such systems are usually employed in injecting the fuel to direct injection engines such as diesel engines.
Typically, fuel injection systems of the above type include a common rail in which fuel pressurized and discharged by a fuel pump is accumulated under high pressure, a rail pressure sensor working to measure the pressure of the fuel in the common rail (which will also be referred to as a rail pressure below), fuel injectors installed in the engine, and a controller working to control injection of the fuel into cylinders of the engine.
The controller monitors outputs from the rail pressure sensor or other sensors to actuate and control the injectors to spray the amount of fuel meeting operating requirements of the engine.
The rail pressure is one of quantities of state of the engine used to calculate commands to be outputted to the injectors which indicate the injection timing and the injection period. If the rail pressure sensor is changed in performance or has failed in operation thereof, it will impinge upon the operation of the engine undesirably.
In order to alleviate the above problem, U.S. Pat. No. 6,705,296 B2 to Horstmann et al. teaches a fuel injection system designed to correct a shift of zero point or offset error of the output of the rail pressure sensor when a given condition is encountered. Specifically, when the rate of drop of temperature of cooling water of the engine exceeds a given threshold level, e.g., when the engine is at rest, the system works to correct the offset error. The time the offset error is to be corrected may be determined using an output of a coolant temperature sensor in an inexpensive and simple manner.
The above system, however, can make the correction of the offset error only when the given condition is met. The number of the corrections is, therefore, not always sufficient for ensuring the stability of operation of the engine. The system is designed only to correct the offset error of the output of the rail pressure sensor and cannot always assure the stability of operation of the engine if another problem, such as a change in performance or a failure in operation of the rail pressure sensor, has occurred.